JP5946096B2 - A novel visible light responsive photocatalyst with environmental resistance - Google Patents
A novel visible light responsive photocatalyst with environmental resistance Download PDFInfo
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- JP5946096B2 JP5946096B2 JP2012557994A JP2012557994A JP5946096B2 JP 5946096 B2 JP5946096 B2 JP 5946096B2 JP 2012557994 A JP2012557994 A JP 2012557994A JP 2012557994 A JP2012557994 A JP 2012557994A JP 5946096 B2 JP5946096 B2 JP 5946096B2
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- tungsten oxide
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- copper
- environmental resistance
- tungsten
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- 239000011941 photocatalyst Substances 0.000 title claims description 50
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Description
本発明は、環境耐性のある新規な可視光応答性光触媒に関するものである。 The present invention relates to a novel visible light responsive photocatalyst having environmental resistance.
近年、太陽光や室内光によって環境汚染物質を吸着し分解除去したり、表面に付着した汚れに対してセルフクリーニング作用を示したりする光触媒が注目され、その研究が精力的に行われている。酸化チタンはその代表的なものであり強力な光触媒活性を示す。しかし、酸化チタンはバンドギャップが大きいため太陽光の大部分を占める可視光には吸収性がなく、紫外光による光触媒活性を示すが、可視光による活性を示さない。そのため太陽光を十分に利用することができず、また紫外光が極めて弱い室内では機能しないという問題があった。 In recent years, photocatalysts that adsorb and decompose and remove environmental pollutants by sunlight or indoor light, or that exhibit a self-cleaning action against dirt adhering to the surface have attracted attention, and their research has been vigorously conducted. Titanium oxide is a typical example and exhibits strong photocatalytic activity. However, since titanium oxide has a large band gap, visible light occupying most of sunlight is not absorptive and exhibits photocatalytic activity by ultraviolet light, but does not exhibit activity by visible light. For this reason, there is a problem that sunlight cannot be used sufficiently and it does not function in a room where ultraviolet light is extremely weak.
その対策として、窒素ドープなどで可視光を吸収できるようにするなどの酸化チタンの改良研究や可視光で光触媒としての活性を示す酸化チタン以外の新規な酸化物半導体の探索研究などが行われており、酸化チタンに比較してバンドギャップが小さいために可視光を吸収することができる酸化タングステンなどの可視光応答性の半導体化合物がCuOやCuBi2O4、銅イオン、白金、パラジウムなどの適切な助触媒を混合ないしその表面に担持させることで可視光活性な光触媒（可視光応答性光触媒）として効率良く働くことが知られている（特許文献１等）。As countermeasures, research on improving titanium oxide, such as allowing nitrogen to absorb visible light, and research on new oxide semiconductors other than titanium oxide that show photocatalytic activity in visible light, etc., have been conducted. Since the band gap is small compared to titanium oxide, visible light-responsive semiconductor compounds such as tungsten oxide that can absorb visible light are suitable, such as CuO, CuBi 2 O 4 , copper ions, platinum, and palladium. It is known that an effective cocatalyst works as a visible light active photocatalyst (visible light responsive photocatalyst) by mixing or supporting on the surface thereof (
しかしながら、これらの半導体化合物および助触媒は、アルカリ性や酸性などの過酷な条件下では不安定な物質が多いため、応用範囲が限定されていた。例えば、酸化タングステンはアルカリ性で溶解しやすいため、流し台などアルカリ性の洗剤が使用される場所においてそのままでは用いることができない。そのため、家庭の水回りなど様々な用途に利用するために、アルカリ性や酸性などの条件下でも安定な可視光応答性の光触媒が望まれていた。 However, since these semiconductor compounds and cocatalysts are often unstable under harsh conditions such as alkalinity and acidity, their application range is limited. For example, since tungsten oxide is alkaline and easily dissolved, it cannot be used as it is in a place where an alkaline detergent is used such as a sink. For this reason, a visible light responsive photocatalyst that is stable even under alkaline or acidic conditions has been desired for use in various applications such as household water.
またアルカリ性や酸性などの条件下で不安定な物質を安定に使うために、従来から様々な検討がなされてきた。例えば、基材表面に耐アルカリ性に優れた光触媒層を形成するために、ジルコニウム、チタン、アルミニウムなどの化合物を含んだ樹脂で基材上にプライマリー皮膜を形成してからジルコニウムやチタンの化合物を含む組成物による中間層をさらに形成し、その上に光触媒粒子およびバインダーとしてのジルコニウム化合物を含有する組成物によって光触媒層を形成することにより、光触媒層が基材から脱落するのを防止する方法が報告されている（特許文献２）。また抗菌性光触媒性塗料の耐アルカリ性を向上させるため、光触媒を含有する水系塗料にポリオルガノシロキサンおよびアクリルポリマーを添加して複合化する方法やアクリルシリコン塗料に光触媒乾燥粉末を含有させる方法も報告されている（特許文献３および４）。
これらは安定な物質で基材表面あるいは光触媒を被覆してアルカリから保護する方法である。しかし、光触媒反応のためには、光照射で生成する正孔と電子が外表面へ到達し、そこで正孔が有機物などの反応基質を酸化分解し、電子が空気中の酸素の還元により消費されることが必要であるが、光触媒をこのような被覆により保護した場合は、正孔も電子もともに同じく新たに被覆した保護物質層を通り抜けてその表面で基質や酸素と反応しなければないため、電荷分離が効率的に促進されず途中で正孔と電子が再結合する、被覆した物質の表面の反応性が低い等のために光触媒活性が低下するなどの問題がある。またさらに被覆を行うために複雑な過程を要しコストが増大することや使用目的に即した、望んでいる被覆構造を容易に得られないことも問題となる。
These are methods of protecting the substrate surface or photocatalyst with a stable substance from alkali. However, for photocatalytic reaction, holes and electrons generated by light irradiation reach the outer surface, where holes oxidize and decompose reaction substrates such as organic substances, and electrons are consumed by reduction of oxygen in the air. However, when the photocatalyst is protected by such a coating, both holes and electrons must pass through the newly coated protective material layer and react with the substrate and oxygen on the surface. There are problems such that charge separation is not efficiently promoted and holes and electrons are recombined in the middle, and the photocatalytic activity is lowered due to low reactivity of the surface of the coated substance. In addition, a complicated process is required to perform the coating, resulting in an increase in cost and a difficulty in obtaining a desired coating structure in accordance with the purpose of use.
本発明は、可視光応答性半導体自体のアルカリ性条件下における環境耐性を向上させた、新規な可視光応答性光触媒を提供することを課題とする。 An object of the present invention is to provide a novel visible light responsive photocatalyst that improves the environmental resistance of the visible light responsive semiconductor itself under alkaline conditions.
本発明者らは、上記課題を解決するために鋭意検討した結果、アルカリ性条件下で不安定な可視光応答性半導体に他の元素を添加することにより、可視光に対する光触媒機能を失わせずにその環境耐性を向上させ得ることを見出し、上記の課題を解決した。具体的には、アルカリ条件下で不安定な酸化タングステンに銅、タンタル、ニオブ、ランタン、ビスマス、カルシウム、クロム、マンガン、亜鉛を単独もしくは複合して添加することにより、その光触媒機能を失わせずにアルカリ性条件下における環境耐性を向上させることに成功した。さらに、ビスマスを添加した場合には条件によって光触媒活性が向上することを見出した。
また、本発明者らは、酸化タングステンに銅、タンタル、ニオブ、ランタン、ビスマス、カルシウム、クロム、マンガン、亜鉛を単独もしくは複合して添加した光触媒を更にアルカリ処理することにより、光触媒活性が向上することを見出した。As a result of intensive studies to solve the above-mentioned problems, the present inventors have added other elements to a visible light-responsive semiconductor that is unstable under alkaline conditions, so that the photocatalytic function for visible light is not lost. The present inventors have found that the environmental resistance can be improved and solved the above problems. Specifically, by adding copper, tantalum, niobium, lanthanum, bismuth, calcium, chromium, manganese, or zinc alone or in combination to tungsten oxide that is unstable under alkaline conditions, its photocatalytic function is not lost. Has succeeded in improving environmental resistance under alkaline conditions. Furthermore, when bismuth was added, it discovered that photocatalytic activity improved with conditions.
In addition, the present inventors further improve the photocatalytic activity by further alkali treatment of a photocatalyst obtained by adding copper, tantalum, niobium, lanthanum, bismuth, calcium, chromium, manganese, or zinc alone or in combination to tungsten oxide. I found out.
すなわち、この出願は、以下の発明を提供するものである。
〈１〉酸化タングステンにタンタル、ランタン、ビスマス、カルシウムの元素を単独もしくは複合して添加することにより、酸化タングステンの可視光による光触媒機能を失わせずにアルカリ性条件下における環境耐性を向上させる方法であって、前記酸化タングステンの前駆体に前記元素の少なくともいずれかを加えて混合して焼成する工程、前記酸化タングステンの粉末に前記元素の少なくともいずれかを含む溶液を含浸して焼成する工程、及び前記酸化タングステンの膜に前記溶液を塗布して焼成する工程のいずれかの焼成工程を含むことを特徴とする方法。
〈２〉添加する上記の元素の量がタングステンに対するモル比で０.００５〜０.５０である、〈１〉に記載の方法。
〈３〉添加する上記の元素の量がタングステンに対するモル比で０.０１〜０.１５である、〈２〉に記載の方法。
〈４〉酸化タングステンにビスマスを添加し、４００〜７００℃で焼成することにより、光触媒活性を向上させることを特徴とする、〈１〉〜〈３〉のいずれかに記載の方法。
〈５〉焼成工程後、更に焼成物をアルカリ処理することにより光触媒活性を向上させる〈１〉〜〈４〉のいずれかに記載の方法。
〈６〉酸化タングステン光触媒中にタンタル、ランタン、ビスマス及びカルシウムの少なくともいずれかの元素が添加されることを特徴とする光触媒。
That is, this application provides the following invention.
<1> tantalum tungsten oxide, La lanthanum, bismuth, by an element of the calcium is added alone or in combination, to improve the environmental resistance in alkaline conditions without losing the photocatalytic function by visible light of the tungsten oxide A method in which at least one of the elements is added to the tungsten oxide precursor and mixed and fired, and the tungsten oxide powder is impregnated with a solution containing at least one of the elements and fired. And a baking step of applying and baking the solution onto the tungsten oxide film.
<2> The method according to <1>, wherein the amount of the element added is 0.005 to 0.50 in terms of a molar ratio to tungsten.
<3> The method according to <2>, wherein the amount of the element added is 0.01 to 0.15 in terms of a molar ratio to tungsten.
<4> The method according to any one of <1> to <3>, wherein the photocatalytic activity is improved by adding bismuth to tungsten oxide and baking at 400 to 700 ° C.
<5> The method according to any one of <1> to <4>, wherein after the firing step, the fired product is further alkali-treated to improve the photocatalytic activity.
<6> tantalum in the tungsten oxide photocatalyst, La lanthanum, photocatalyst, characterized in that at least one of the elements bismuth and calcium are added.
酸化タングステンは酸性条件下で安定な可視光応答性光触媒である。本発明により、アルカリ性条件下においても安定で環境耐性のある新規な酸化タングステン可視光応答性光触媒が提供される。
本発明による新規な可視光応答性光触媒は、アルカリ性や酸性の条件下においても安定なため、流し台、浴室、トイレなどにおいて洗剤や漂白剤などに曝されることによってアルカリ性や酸性の環境となる場合でも使用することができる。これらの設備は屋内にあることがほとんどなので、そこで光触媒製品を用いる場合には太陽の紫外光による光触媒作用が期待できないため、屋内の可視光によって機能する可視光応答性光触媒が必要となるが、本発明により環境耐性を向上させることで、これまではこれらの設備では使用できなかった酸化タングステン可視光応答性光触媒を使用することが可能になる。本発明の酸化タングステンを使用することにより表面が有機物で汚染されてもその光触媒作用によるセルフクリーニング機能で汚れが分解除去され表面を清浄に保持することができる。Tungsten oxide is a visible light responsive photocatalyst that is stable under acidic conditions. The present invention provides a novel tungsten oxide visible light responsive photocatalyst that is stable and environmentally resistant even under alkaline conditions.
Since the novel visible light responsive photocatalyst according to the present invention is stable even under alkaline or acidic conditions, it becomes an alkaline or acidic environment when exposed to detergents or bleaches in a sink, bathroom, toilet, etc. But it can be used. Most of these facilities are indoors, so when using photocatalytic products, photocatalysis by solar ultraviolet light cannot be expected, so a visible light-responsive photocatalyst that functions by indoor visible light is required. By improving the environmental resistance according to the present invention, it becomes possible to use a tungsten oxide visible light responsive photocatalyst that could not be used in these facilities until now. By using the tungsten oxide of the present invention, even if the surface is contaminated with an organic substance, dirt is decomposed and removed by the self-cleaning function by the photocatalytic action, and the surface can be kept clean.
１ 可視光応答性光触媒内部
２ 添加により環境耐性が増加した表面
３ 分解する吸着物質
４ 助触媒
５ 正孔
６ 励起電子1 Visible light responsive photocatalyst inside 2 Surface with increased environmental resistance due to
本発明では、アルカリ性条件下で不安定な可視光応答性半導体にアルカリ性条件下で安定な元素を添加することで環境耐性を向上させる。図１の模式図に示すように、アルカリ性条件下で安定な元素を添加することにより、可視光応答性半導体の少なくとも表面がアルカリ性条件下で安定な構造となり、それにより不安定であった可視光応答性半導体全体が保護されて環境耐性が向上すると考えられる。本発明による可視光応答性光触媒は環境耐性のある助触媒と組み合わせて用いることができる。特に有機物の完全酸化分解を行う場合は酸素還元を促進する助触媒を担持することが好ましい。助触媒としては酸素還元を促進する、白金、パラジウムなどの貴金属や銅化合物などが用いられる。助触媒を担持する場所は、半導体膜の外表面や多孔質膜の内部や底部でもよい。
さらに酸化チタンのような、環境耐性があり、表面における正孔の反応性も高いものによって本発明の外表面を被覆して用いることもできる。そのような場合は、本発明と被覆との相乗効果を期待することができる。
環境耐性を向上させるために他の元素を添加した酸化タングステンは、水酸化ナトリウム水溶液などに一定時間浸漬することによるアルカリ処理を行うことで光触媒活性が向上する。処理するアルカリの濃度や処理時間は添加する元素の種類・量や酸化タングステンの形状などにより異なるため、適宜最適な条件により行う必要があるが、一般的には、水酸化ナトリウム水溶液を処理に用いる場合の濃度は、望ましくは０.０１Ｍ〜３.０Ｍ、より望ましくは０.１Ｍ〜２.０Ｍ、また浸漬処理時間は１０分から１０時間、さらに望ましくは３０分から６時間である。In the present invention, environmental resistance is improved by adding an element which is stable under alkaline conditions to a visible light responsive semiconductor which is unstable under alkaline conditions. As shown in the schematic diagram of FIG. 1, by adding an element that is stable under alkaline conditions, at least the surface of the visible light-responsive semiconductor has a stable structure under alkaline conditions. It is considered that the entire responsive semiconductor is protected and the environmental resistance is improved. The visible light responsive photocatalyst according to the present invention can be used in combination with an environmentally resistant promoter. In particular, when carrying out complete oxidative decomposition of organic matter, it is preferable to support a promoter that promotes oxygen reduction. As the cocatalyst, a noble metal such as platinum or palladium or a copper compound that promotes oxygen reduction is used. The place for supporting the promoter may be the outer surface of the semiconductor film, the inside or the bottom of the porous film.
Furthermore, the outer surface of the present invention can be used by being coated with a material having environmental resistance such as titanium oxide and having high hole reactivity on the surface. In such a case, a synergistic effect between the present invention and the coating can be expected.
Tungsten oxide to which other elements are added to improve environmental resistance is improved in photocatalytic activity by performing an alkali treatment by immersing in an aqueous sodium hydroxide solution for a certain period of time. Since the concentration of alkali to be treated and the treatment time vary depending on the type and amount of element to be added and the shape of tungsten oxide, etc., it is necessary to carry out the treatment under optimum conditions as appropriate. The concentration in this case is preferably 0.01 M to 3.0 M, more preferably 0.1 M to 2.0 M, and the immersion treatment time is 10 minutes to 10 hours, and more preferably 30 minutes to 6 hours.
現在のところ、環境耐性が向上する表面の詳細な構造は不明であるが、以下のような可能性が考えられる。添加された元素が可視光応答性半導体全体にドープされ、そのドープ構造の安定性がアルカリ性においても高いために環境耐性が向上すると考えられる。この場合には全体として元の可視光応答性半導体の割合が添加された元素に比較して大きいため、元の光触媒機能が失われないと考えられる。
別の可能性としては、新たに生成した光触媒の内部に添加した元素を含まない元の可視光応答性半導体の構造の部分がそのまま残って光触媒機能が保持されているのに対して、表面近くでは添加した元素の割合が大きく、元の半導体の成分と合わさって複合酸化物などの複合化合物を形成し、外部の環境に対して保護する作用をしていることも考えられる。この場合は少なくとも環境耐性が向上している表面において、光触媒機能により生成する正孔と電子がそれぞれ反応基質や空気中の酸素と容易に反応できる必要がある。ただし光の吸収と正孔および電子の生成は、内部に元の可視光応答性半導体構造が残っていた場合などはその部分で機能してもよく、そのような場合にはそこで発生した正孔と電子が表面まで移動して反応する。
さらに別の可能性としては、添加した元素の影響で可視光応答性半導体粒子が大きくなることによって比表面積が減少し、アルカリ性の環境においても溶解しにくくなることが考えられる。添加により可視光応答性半導体の１次粒子が大きくなるとそれが凝集して形成される粒子も表面積が減少するため溶解しにくくなる。
これらの要因が複合的に寄与して全体としてアルカリ性条件下における環境耐性が向上していることも考えられる。At present, the detailed structure of the surface that improves environmental resistance is unknown, but the following possibilities are conceivable. The added element is doped in the entire visible light responsive semiconductor, and the stability of the doped structure is high even in alkalinity, so that it is considered that the environmental resistance is improved. In this case, it is considered that the original photocatalytic function is not lost because the ratio of the original visible light responsive semiconductor as a whole is larger than the added element.
Another possibility is that the structure of the original visible light-responsive semiconductor that does not contain the added element inside the newly generated photocatalyst remains as it is, and the photocatalytic function is retained, but it is close to the surface. Then, it is conceivable that the ratio of the added element is large, and a composite compound such as a composite oxide is formed by combining with the original semiconductor components, thereby protecting the external environment. In this case, it is necessary that holes and electrons generated by the photocatalytic function can easily react with the reaction substrate and oxygen in the air at least on the surface having improved environmental resistance. However, light absorption and generation of holes and electrons may function in that part, such as when the original visible light responsive semiconductor structure remains inside, in which case holes generated there And electrons react to move to the surface.
As another possibility, it is conceivable that the specific surface area decreases due to the increase in visible light-responsive semiconductor particles due to the effect of the added element, and it becomes difficult to dissolve even in an alkaline environment. When the primary particles of the visible light responsive semiconductor become larger due to the addition, the particles formed by agglomeration thereof are also difficult to dissolve because the surface area is reduced.
It is conceivable that the environmental resistance under alkaline conditions is improved as a whole due to a combination of these factors.
以下に、アルカリ性条件下では溶解する酸化タングステンの環境耐性を、光触媒機能を失わせることなく向上させるため、ＰＡ法（過酸化物の熱分解法）により酸化タングステンを製造するときに銅を添加する方法に関して説明する。ただし、後に示すように本発明は特定の製造方法に何ら限定されるものではない。
最初にタングステン酸または金属タングステンなどのタングステン含有材料を過酸化水素水溶液に溶解させたのち乾燥させる。得られた白色結晶を水で再度溶解させホットスターラー上で撹拌・加熱を行いながら熟成させ濃いオレンジ色の過酸化ポリタングステンを生成させる。これに銅が所定の添加量となるように硝酸銅を加えて焼成することで銅を添加した酸化タングステンを得る。このように酸化タングステンの製造過程において銅化合物を添加するという単純な方法で本発明を実施することができる。
本方法により得られる、銅を添加した酸化タングステンは、アルカリ性条件下における環境耐性が向上するとともに可視光による光触媒機能が失われない。
このとき添加する銅の割合は、望ましくはタングステンに対してモル比（Cu/Wモル比）で０.００５〜０.５０、より望ましくは０.０１〜０.１５であるが、必要とされる環境耐性の向上度は光触媒としての使用目的・使用条件によって異なるため、状況により適宜決定される。また、好ましい添加量は添加する元素や添加方法によっても異なる。Below, in order to improve the environmental resistance of tungsten oxide that dissolves under alkaline conditions without losing the photocatalytic function, copper is added when producing tungsten oxide by the PA method (peroxide pyrolysis method). The method will be described. However, as will be described later, the present invention is not limited to a specific manufacturing method.
First, a tungsten-containing material such as tungstic acid or metallic tungsten is dissolved in an aqueous hydrogen peroxide solution and then dried. The obtained white crystals are redissolved with water and aged while being stirred and heated on a hot stirrer to produce dark orange polytungsten peroxide. Tungsten oxide to which copper is added is obtained by adding copper nitrate and firing so that the copper is added in a predetermined amount. Thus, the present invention can be implemented by a simple method of adding a copper compound in the process of producing tungsten oxide.
The tungsten oxide added with copper obtained by this method has improved environmental resistance under alkaline conditions and does not lose its photocatalytic function by visible light.
The ratio of copper added at this time is preferably 0.005 to 0.50, more preferably 0.01 to 0.15 in terms of molar ratio (Cu / W molar ratio) to tungsten, but is required. Since the degree of improvement in environmental resistance varies depending on the purpose and conditions of use as a photocatalyst, it is appropriately determined depending on the situation. Moreover, a preferable addition amount changes also with the element to add and the addition method.
光触媒活性を示す化合物の環境耐性を向上させる目的で他の元素をその製造過程において何らかの方法によって添加する場合を考えると、通常は、添加量が少なすぎると環境耐性があまり向上せず、また添加量が多すぎると環境耐性が十分向上しても光触媒機能そのものがそれによって著しく低下する又は失われてしまうと考えられる。また一般には、他の元素の添加量を増やしていった場合に、環境耐性が必要とされるだけ向上する前に光触媒機能が全く失われてしまうことも十分に考えられる。しかしながら本発明者らは、酸化タングステンの製造過程において銅などの本発明に示す元素を単独でもしくは複合して添加した場合は、その光触媒機能を失わせることなくアルカリ性条件下における環境耐性の向上を実現できることを見いだして本発明を成すに至った。
また、ビスマスなどの特定の元素は、一定条件で酸化タングステンに添加することにより、環境耐性の向上のみならず、無添加の酸化タングステンに比較して光触媒活性が向上することも見出した。Considering the case where other elements are added by some method in the production process for the purpose of improving the environmental resistance of the compound exhibiting photocatalytic activity, the environmental resistance is usually not improved much if the addition amount is too small. If the amount is too large, it is considered that even if the environmental resistance is sufficiently improved, the photocatalytic function itself is remarkably lowered or lost. In general, when the amount of addition of other elements is increased, it is sufficiently conceivable that the photocatalytic function is completely lost before the environmental resistance is improved as much as necessary. However, the present inventors have improved the environmental resistance under alkaline conditions without losing the photocatalytic function when the elements shown in the present invention such as copper are added alone or in combination in the production process of tungsten oxide. The inventors have found that it can be realized and have come up with the present invention.
In addition, it has also been found that addition of a specific element such as bismuth to tungsten oxide under certain conditions not only improves environmental resistance, but also improves the photocatalytic activity as compared to additive-free tungsten oxide.
さらに単にアルカリ性条件下で安定な元素を添加することによってアルカリ性条件下で不安定な物質の環境耐性が必ずしも向上するものではない。酸化タングステンの場合も、アルカリ性条件下における環境耐性を向上させることを目指してアルカリ性条件下で安定な元素を添加してもすべてにおいてその向上が見られるわけではなく（後述の比較例６）、本発明では銅などの本発明に示す元素の単独もしくは複合の添加においてこの目的を達成することができた。故に本発明の酸化タングステンとこれらの元素の組み合わせは課題解決に対して特に優れたものである。 Furthermore, simply adding an element that is stable under alkaline conditions does not necessarily improve the environmental resistance of substances that are unstable under alkaline conditions. Even in the case of tungsten oxide, even if an element that is stable under alkaline conditions is added in order to improve environmental resistance under alkaline conditions, the improvement is not observed in all (Comparative Example 6 described later). In the invention, this object can be achieved by adding a single element or a complex element of the present invention such as copper. Therefore, the combination of tungsten oxide and these elements of the present invention is particularly excellent for solving the problems.
また本発明においては、具体的な添加方法を変えても光触媒機能を失わせることなく環境耐性の向上を実現できることを見いだしている。このことは、製造方法が異なっても光触媒製造過程において酸化タングステンに銅を添加することによって最終的に同じような構造が生成するためと考えられる。以下の実施例にも示すように、酸化タングステンについては、ＰＡ法・ＩＥ法（イオン交換法）・錯体重合法などの様々な光触媒製造法があるが、これらのどの方法も本発明による銅の添加ために用いることができる。これらの製造方法の場合は、酸化タングステンの前駆体に銅の金属塩を加えて混合してから焼成することにより銅を添加することができる。通常、焼成温度は、単にこれらの製造方法により酸化タングステンを製造する場合と同じで良く、望ましくは４００℃〜９００℃、より望ましくは５００℃〜８００℃である。またさらに酸化タングステン粉末試料に銅の金属塗布液を含浸して焼成することによっても本発明を実施することができる。この場合には、粉末表面に添加された銅が焼成により原子レベルで酸化タングステンと混ざり合う必要があるため、焼成は比較的高温で行う必要があり、望ましくは６００℃〜９００℃、より望ましくは７５０℃〜８５０℃である。一般に、銅以外の元素の添加に関してもこれらの様々な製造方法を同様に用いることができるが、好ましい焼成温度などの条件は添加する元素によって異なる。また前記したような前駆体溶液などを基板上に塗布・焼成して作製した酸化タングステン薄膜に、添加する元素を含んだ金属塗布液を塗布してさらに焼成する方法によっても実施することができる。このような薄膜形状の場合の焼成温度は、添加する元素の種類にもよるが、粉末形状の場合とは一般には異なっており、望ましくは４００℃〜６００℃、より望ましくは４５０℃〜５５０℃である。このような場合には焼成温度の上限は基板の耐熱性の上限で決まることが多く、基板が耐えられる場合は９００℃程度の高温でも焼成することが可能である。 Further, in the present invention, it has been found that even if the specific addition method is changed, the environmental resistance can be improved without losing the photocatalytic function. This is considered to be because even if the manufacturing method is different, the same structure is finally formed by adding copper to tungsten oxide in the photocatalyst manufacturing process. As shown in the following examples, there are various photocatalyst production methods such as PA method, IE method (ion exchange method), and complex polymerization method for tungsten oxide. Can be used for addition. In the case of these manufacturing methods, copper can be added by adding and mixing a copper metal salt to a tungsten oxide precursor, followed by firing. Usually, the firing temperature may be the same as that for producing tungsten oxide simply by these production methods, preferably 400 ° C to 900 ° C, more preferably 500 ° C to 800 ° C. Further, the present invention can also be implemented by impregnating a tungsten oxide powder sample with a copper metal coating solution and baking it. In this case, since the copper added to the powder surface needs to be mixed with tungsten oxide at an atomic level by firing, firing must be performed at a relatively high temperature, preferably 600 ° C. to 900 ° C., more preferably 750-850 degreeC. In general, these various production methods can be used similarly for addition of elements other than copper, but preferable conditions such as the firing temperature differ depending on the elements to be added. It can also be carried out by a method in which a metal coating solution containing the element to be added is applied to a tungsten oxide thin film prepared by applying and firing the precursor solution as described above on the substrate and then further fired. The firing temperature in the case of such a thin film shape depends on the type of element to be added, but is generally different from that in the case of a powder shape, preferably 400 ° C. to 600 ° C., more preferably 450 ° C. to 550 ° C. It is. In such a case, the upper limit of the baking temperature is often determined by the upper limit of the heat resistance of the substrate, and if the substrate can withstand, baking can be performed at a high temperature of about 900 ° C.
以下に、具体的な実施例を用いて、本発明をさらに詳細に説明する。 Hereinafter, the present invention will be described in more detail using specific examples.
〈銅添加によるアルカリ性条件下における環境耐性の向上について〉
実施例１および比較例１ ＰＡ法
アルカリ性条件下では溶解する酸化タングステンにアルカリ性条件下で安定な銅をタングステンに対してモル比（Cu/Wモル比）で０.１３添加した可視光応答性銅添加酸化タングステン光触媒を下記のＰＡ法で調製して、実施例１とした。またこの方法で製造した銅を添加しない酸化タングステンを比較例１とした。
金属タングステンを過酸化水素水溶液に溶解して乾燥させたものを水で再溶解し、さらにホットスターラー上で撹拌・加熱を行いながら熟成させ透明黄色溶液を経て濃いオレンジ色の過酸化ポリタングステンを生成させる。次に銅がタングステンに対してモル比（Cu/Wモル比）で０.１３となるように硝酸銅を添加する。この操作により生成する、銅が添加された過酸化ポリタングステンを８００℃で焼成することで実施例１となる銅を添加した酸化タングステンが得られる。
実施例１（銅をタングステンに対してモル比（Cu/Wモル比）で０.１３添加した酸化タングステン）および比較例１（銅を添加しない酸化タングステン）の粉末を１.０Ｍの水酸化ナトリウム水溶液に投入し、２時間にわたり放置した後に目視で変化を観察した。その結果、比較例１では９割以上が溶解したのに対して、実施例１では見かけ上はまったく変化がなかった。実施例１では明らかに銅を添加することによりアルカリ性条件下における酸化タングステンの環境耐性が向上している。<Improvement of environmental resistance under alkaline conditions by adding copper>
Example 1 and Comparative Example 1 PA Method Visible-light-responsive copper obtained by adding 0.13 of a stable ratio of tungsten to tungsten oxide, which dissolves under alkaline conditions, to the tungsten in a molar ratio (Cu / W molar ratio). An added tungsten oxide photocatalyst was prepared by the following PA method, and was used as Example 1. Moreover, the tungsten oxide which does not add the copper manufactured by this method was made into the comparative example 1.
Metal tungsten dissolved in hydrogen peroxide solution and dried, redissolved with water, and aged with stirring and heating on a hot stirrer to produce a deep orange polytungsten peroxide through a transparent yellow solution Let Next, copper nitrate is added so that the molar ratio of copper to tungsten (Cu / W molar ratio) is 0.13. By baking the polytungsten peroxide to which copper is added, which is generated by this operation, at 800 ° C., tungsten oxide to which copper is added as in Example 1 is obtained.
The powder of Example 1 (tungsten oxide added with 0.13 molar ratio of copper to tungsten (Cu / W molar ratio)) and Comparative Example 1 (tungsten oxide without added copper) was added to 1.0M sodium hydroxide powder. It was poured into an aqueous solution and allowed to stand for 2 hours, and then the change was visually observed. As a result, in Comparative Example 1, 90% or more was dissolved, whereas in Example 1, there was no apparent change at all. In Example 1, the environmental resistance of tungsten oxide under alkaline conditions is obviously improved by adding copper.
実施例２および比較例２ ＩＥ法
銅添加酸化タングステン光触媒の調製法を以下に示すＩＥ法に変更して、実施例２とした。０.５Ｍのタングステン酸ナトリウム水溶液２０ｍｌをイオン交換樹脂に通してエタノールに滴下し、タングステン酸のエタノール・水混合溶液を調製し、ポリエチレングリコール３００を５ｍｌ添加する。さらにこの溶液に硝酸銅水溶液を撹拌しながらタングステンに対してモル比（Cu/Wモル比）で０.１３となるように添加する。この溶媒を蒸発させ、さらに６５０℃で1時間加熱することで実施例２となる銅添加酸化タングステンが得られる。またこの方法で製造した銅を添加しない酸化タングステンを比較例２とした。
この実施例２（銅をタングステンに対してモル比（Cu/Wモル比）で０.１３添加した酸化タングステン）および比較例２（銅を添加しない酸化タングステン）を１.０Ｍの水酸化ナトリウム水溶液に投入し安定性の比較を行った。その結果、比較例２は３時間で完全に溶解したのに対して、実施例２は３時間後においても濾過後の残存重量として６８％以上が溶け残った。実施例２においても明らかに銅を添加することによりアルカリ性条件下における酸化タングステンの環境耐性が向上している。Example 2 and Comparative Example 2 IE Method The method for preparing the copper-added tungsten oxide photocatalyst was changed to the IE method shown below to obtain Example 2. 20 ml of 0.5 M sodium tungstate aqueous solution is passed through an ion exchange resin and dropped into ethanol to prepare a mixed solution of tungstic acid in ethanol and water, and 5 ml of
This Example 2 (tungsten oxide added with 0.13 molar ratio of copper to tungsten (Cu / W molar ratio)) and Comparative Example 2 (tungsten oxide without added copper) were added to a 1.0M sodium hydroxide aqueous solution. The stability was compared. As a result, Comparative Example 2 was completely dissolved in 3 hours, whereas in Example 2, 68% or more remained as a residual weight after filtration even after 3 hours. Also in Example 2, the environmental resistance of tungsten oxide under alkaline conditions is improved by clearly adding copper.
実施例３および比較例３ 錯体重合法
銅添加酸化タングステン光触媒の調製法を以下に示す錯体重合法に変更して、実施例３とした。タングステン酸アンモニウムとクエン酸をエチレングリコールとメタノールの混合溶液に溶解し、さらに硝酸銅水溶液を撹拌しながらタングステンに対してモル比（Cu/Wモル比）が０.１３、０.０６、０.０５となるように添加する。この溶媒を蒸発させ、６５０℃で1時間加熱することで実施例３となる銅添加酸化タングステンが得られる。またこの方法で製造した銅を添加しない酸化タングステンを比較例３とした。
この実施例３（銅をタングステンに対してモル比（Cu/Wモル比）で０.１３、０.０６、０.０５添加した酸化タングステン）および比較例３（銅を添加しない酸化タングステン）を１.０Ｍの水酸化ナトリウム水溶液に投入し安定性の比較を行った。その結果、比較例３では、３時間後に濾過後の残存重量として溶け残ったのは２０％であった。一方、実施例３では、６時間後においても濾過後の残存重量として、銅の添加量がタングステンに対してモル比（Cu/Wモル比）で０.１３、０.０６、０.０５の場合それぞれについて、９２％、８６％、７９％が溶け残った。実施例３においても明らかに銅を添加することによりアルカリ性条件下における酸化タングステンの環境耐性が向上している。Example 3 and Comparative Example 3 Complex Polymerization Method Example 3 was prepared by changing the preparation method of the copper-added tungsten oxide photocatalyst to the complex polymerization method shown below. Ammonium tungstate and citric acid are dissolved in a mixed solution of ethylene glycol and methanol, and the molar ratio (Cu / W molar ratio) with respect to tungsten is 0.13, 0.06, 0.0 while stirring the aqueous copper nitrate solution. Add to 05. By evaporating the solvent and heating at 650 ° C. for 1 hour, the copper-added tungsten oxide of Example 3 is obtained. Moreover, the tungsten oxide which does not add the copper manufactured by this method was made into the comparative example 3.
Example 3 (tungsten oxide added with 0.13, 0.06, 0.05 in molar ratio of copper to tungsten (Cu / W molar ratio)) and Comparative Example 3 (tungsten oxide without added copper) The stability was compared by adding it to a 1.0 M sodium hydroxide aqueous solution. As a result, in Comparative Example 3, 20% remained undissolved as the remaining weight after filtration after 3 hours. On the other hand, in Example 3, the residual weight after filtration even after 6 hours was 0.13, 0.06, 0.05 in terms of molar ratio (Cu / W molar ratio) with respect to tungsten. In each case, 92%, 86% and 79% remained undissolved. Also in Example 3, the environmental resistance of tungsten oxide under alkaline conditions is clearly improved by adding copper.
実施例４および比較例４〜６ 酸化タングステン粉末試料への銅添加
酸化タングステン粉末に後から銅を添加した場合についても調べるために、酸化タングステン粉末（和光純薬工業）に、高純度化学研究所より購入した銅の金属塗布液（SYMETRIX、SYM-CU04、EMOD塗布型材料CuO膜用、銅含有量０.４Ｍ）を酢酸ブチルで２倍に希釈してタングステンに対するモル比で０.０５となるように混合し、８００℃で１時間焼成することにより調製した銅添加タングステンを実施例４とした。また酸化タングステン粉末（和光純薬工業）そのままのものを比較例４、酸化タングステン粉末（和光純薬工業）をそのまま８００℃で１時間焼成しただけのものを比較例５、同じく高純度化学研究所より購入した、アルカリ性条件下で安定な元素であるインジウムの金属塗布液（SYMETRIX、SYM-IN02、EMOD塗布型材料InO1.5膜用、インジウム含有量０.２Ｍ）を銅の代わりにモル比で０.０５となるように混合し、８００℃で１時間焼成することにより調製したインジウム添加タングステンを比較例６とした。
これらを１.０Ｍの水酸化ナトリウム水溶液に投入し、３．５時間後に濾過後の残存重量を調べ、アルカリ性条件下における安定性の比較を行った。その結果、比較例４（何も処理しなかった酸化タングステン）では残存重量０％（完全溶解）、比較例５（８００℃で１時間焼成した酸化タングステン）では残存重量２３％、比較例６（インジウムをタングステンに対してモル比（In/Wモル比）で０.０５添加した酸化タングステン）では残存重量９％であったのに対して、実施例４（銅をタングステンに対してモル比（Cu/Wモル比）で０.０５添加した酸化タングステン）では残存重量は８５％となった。このように実施例４においても溶け残る量が明らかに増加しており、銅を添加することによりアルカリ性条件下における酸化タングステンの環境耐性が向上している。
このような含浸と焼成により粉末の酸化タングステンに銅を添加する場合は焼成温度を６００〜９００℃、好ましくは７５０〜８５０℃程度の高温にすることが望ましい。本発明の銅添加の場合は、銅が酸化タングステン表面に単に担持されるのではなく、その内部に浸透してある程度混ざり合う必要があるため焼成を比較的高温で行う必要があり、そのような状況では添加された銅は表面に担持された助触媒としては作用しない。一方、銅を単に助触媒として粉末の酸化タングステン表面に類似の方法で担持する場合は、特許文献１のように５００〜５５０℃程度の、もっと低温度で焼成を行うことにより、酸化タングステン内部に浸透して混ざり合わないようにする必要がある。なお最適な焼成温度は酸化タングステンの形状（粉末・薄膜）や添加する元素の種類等の諸条件により異なる。Example 4 and Comparative Examples 4 to 6 Copper Addition to Tungsten Oxide Powder Sample In order to investigate the case where copper was added to tungsten oxide powder later, high purity chemical research institute was added to tungsten oxide powder (Wako Pure Chemical Industries). Copper metal coating solution purchased from SYMETRIX, SYM-CU04, EMOD coating type material for CuO film, copper content 0.4M is diluted twice with butyl acetate to a molar ratio to tungsten of 0.05. A copper-added tungsten prepared by mixing in the above manner and firing at 800 ° C. for 1 hour was taken as Example 4. Moreover, the tungsten oxide powder (Wako Pure Chemical Industries) as it is is Comparative Example 4, the tungsten oxide powder (Wako Pure Chemical Industries) is simply calcined at 800 ° C. for 1 hour as Comparative Example 5, and the same high purity chemical laboratory. A metal coating solution of indium, which is a stable element under alkaline conditions (SYMETRIX, SYM-IN02, EMOD coating type material for InO 1.5 film, indium content of 0.2M) purchased in a molar ratio of 0 instead of copper. Indium-added tungsten prepared by mixing to 0.05 and firing at 800 ° C. for 1 hour was used as Comparative Example 6.
These were put into a 1.0 M aqueous sodium hydroxide solution, and after 3.5 hours, the remaining weight after filtration was examined to compare the stability under alkaline conditions. As a result, in Comparative Example 4 (tungsten oxide not treated at all), the remaining weight was 0% (complete dissolution), and in Comparative Example 5 (tungsten oxide calcined at 800 ° C. for 1 hour), the remaining weight was 23%, and Comparative Example 6 ( The remaining weight was 9% in the case of tungsten oxide in which 0.05% of indium was added to tungsten at a molar ratio (In / W molar ratio), whereas Example 4 (molar ratio of copper to tungsten ( In the case of tungsten oxide (with 0.05 addition of Cu / W molar ratio), the remaining weight was 85%. Thus, the amount of undissolved residue in Example 4 also clearly increased, and the addition of copper improves the environmental resistance of tungsten oxide under alkaline conditions.
When copper is added to the powdered tungsten oxide by such impregnation and firing, it is desirable that the firing temperature is 600 to 900 ° C, preferably about 750 to 850 ° C. In the case of the copper addition of the present invention, copper is not simply supported on the surface of tungsten oxide, but needs to permeate into the inside and mix to some extent, so firing must be performed at a relatively high temperature. In the situation, the added copper does not act as a promoter supported on the surface. On the other hand, when copper is simply supported on the surface of the powdered tungsten oxide as a cocatalyst by firing at a lower temperature of about 500 to 550 ° C. as in
また何も処理しない比較例４が完全溶解であったのに対して焼成した比較例５では残存重量が２３％で溶け残る量が増加しており、何も添加しなかった場合でも焼成によりアルカリ性条件下における環境耐性の向上が見られる。このことは焼成過程で粒子が結合して成長し、表面積が減少して溶解速度が小さくなったことに起因すると考えられる。しかし銅添加の場合は、実施例４における残存重量が８５％で比較例５の場合の２３％よりもはるかに多い。このことからすると銅添加によるアルカリ性条件下における環境耐性の向上は単なる焼成による表面積の減少以外の要因が大きい。
さらに銅と同じくアルカリ性条件下で安定なインジウムを添加した比較例６では実施例４のようなアルカリ性条件下における環境耐性の大きな向上は見られず、残存重量は何も添加していない比較例５よりも少なく９％であった。このことは酸化タングステンのアルカリ性条件下における環境耐性の向上は単にアルカリ性で安定な元素を添加するだけでは達成できるものではないことを示している。故に酸化タングステンの場合は銅などの本発明に示す元素を添加することが特異的に環境耐性を向上させることに優れていると考えられる。In contrast, Comparative Example 4 in which nothing was treated was completely dissolved, whereas in Comparative Example 5 which was fired, the remaining amount increased at 23%, and even when nothing was added, it was made alkaline by firing. Improved environmental resistance under conditions. This is considered to be due to the fact that particles are bonded and grow in the firing process, the surface area is reduced, and the dissolution rate is reduced. However, in the case of copper addition, the remaining weight in Example 4 is 85%, much higher than 23% in Comparative Example 5. From this, the improvement in environmental resistance under alkaline conditions by adding copper is largely due to factors other than a reduction in surface area due to simple firing.
Further, in Comparative Example 6 in which indium, which is stable under alkaline conditions as in the case of copper, was added, no significant improvement in environmental resistance was observed under alkaline conditions as in Example 4, and no residual weight was added. Less than 9%. This indicates that the improvement in environmental resistance of tungsten oxide under alkaline conditions cannot be achieved simply by adding alkaline and stable elements. Therefore, in the case of tungsten oxide, it is considered that the addition of the element shown in the present invention such as copper is excellent in improving environmental resistance specifically.
〈銅添加の場合の光触媒活性について〉
光触媒活性を調べるため、実施例１において調製した銅をタングステンに対するモル比で０.１３添加した酸化タングステンを０.１Ｍ水酸化ナトリウム水溶液で６時間処理したものに、助触媒として白金を０.１重量％添加し、それらを４.７ｍｌのバイアルびんにおよそ１５０ｍｇ入れ、これにアセトアルデヒドの気体を約８０００ｐｐｍ分加えて３００ＷのＸｅランプで光照射し、ガスクロマトグラフィーにより光分解で生じる二酸化炭素の量の時間変化をモニターした。図２に結果を示す。なお、本例では、存在するアセトアルデヒドが完全に二酸化炭素にまで分解すると、およそ１６０００ｐｐｍの二酸化炭素が理論的に発生する。
図２から分かるように、本発明の実施例１の銅添加酸化タングステンは、０.１Ｍ水酸化ナトリウム水溶液で６時間処理しても、１２０分経過後にはほぼアセトアルデヒドの完全分解近くにまで達している。また比較例１において調製した銅を添加していない酸化タングステンについても水酸化ナトリウム水溶液で処理せずに同様のアセトアルデヒドの光分解を行った結果を図２示す。これと比較すると分解速度が若干遅くはなっているが、実施例１の銅添加酸化タングステンはアルカリ性の条件下に曝された後であっても、光触媒活性を十分に保持しており、アセトアルデヒドを完全分解できることが示された。本実施例では気相中のアセトアルデヒトの分解除去について示したが、本発明の酸化タングステン光触媒を用いて、表面に付着した有機物を分解除去する光触媒作用によるセルフクリーニング機能を発現させることも可能である。なお比較例１において調製した銅を添加していない酸化タングステンは水酸化ナトリウム水溶液で処理すると完全に溶解するため、アルカリ処理後の光触媒活性は測定できない。
また実施例３において調製した、銅をタングステンに対するモル比で０.１３添加した錯体重合法による酸化タングステンを１.０Ｍ水酸化ナトリウム水溶液で３時間処理したものおよび未処理のものに対して同様のアセトアルデヒト分解による二酸化炭素の発生量をモニターした。図３に結果を示す。図３に矢印で示すように、アルカリ処理により光触媒活性が向上することが分かる。<Photocatalytic activity when copper is added>
In order to investigate the photocatalytic activity, tungsten prepared by adding 0.13 of the copper prepared in Example 1 in a molar ratio to tungsten was treated with a 0.1 M aqueous sodium hydroxide solution for 6 hours, and platinum as a cocatalyst was 0.1. The amount of carbon dioxide produced by photolysis by gas chromatography after adding about 8000 ppm of acetaldehyde gas, irradiating with a 300 W Xe lamp, and placing them in a 4.7 ml vial. The time change of was monitored. The results are shown in FIG. In this example, when the existing acetaldehyde completely decomposes into carbon dioxide, approximately 16000 ppm of carbon dioxide is theoretically generated.
As can be seen from FIG. 2, the copper-added tungsten oxide of Example 1 of the present invention reached almost complete decomposition of acetaldehyde after 120 minutes even after treatment with a 0.1 M aqueous sodium hydroxide solution for 6 hours. Yes. In addition, FIG. 2 shows the result of the same photodegradation of acetaldehyde without treating the tungsten oxide prepared in Comparative Example 1 to which copper was not added with an aqueous sodium hydroxide solution. Compared to this, the decomposition rate is slightly slower, but the copper-added tungsten oxide of Example 1 sufficiently retains the photocatalytic activity even after being exposed to alkaline conditions. It was shown that it can be completely decomposed. In this example, the decomposition removal of acetaldehyde in the gas phase was shown, but it is also possible to develop a self-cleaning function by photocatalytic action that decomposes and removes organic substances attached to the surface using the tungsten oxide photocatalyst of the present invention. is there. In addition, since the tungsten oxide which does not add copper prepared in Comparative Example 1 is completely dissolved when treated with an aqueous sodium hydroxide solution, the photocatalytic activity after alkali treatment cannot be measured.
In addition, the same was applied to those prepared in Example 3 in which tungsten oxide by a complex polymerization method in which 0.13 molar ratio of copper to tungsten was added was treated with 1.0 M aqueous sodium hydroxide solution for 3 hours and untreated. The amount of carbon dioxide generated by acetaldehyde degrading was monitored. The results are shown in FIG. As shown by the arrows in FIG. 3, it can be seen that the photocatalytic activity is improved by the alkali treatment.
〈銅以外の元素の添加によるアルカリ性条件下における環境耐性の向上について〉
実施例５〜１２および比較例４〜６ 酸化タングステン粉末試料への銅以外の元素の添加
銅以外の元素の添加効果を調べるため、銅添加の場合と同じように酸化タングステン粉末（和光純薬工業）に、高純度化学研究所より購入した各添加元素の金属塗布液をタングステンに対してモル比で０.０５となるように混合し、８００℃で１時間焼成することにより各試料を調製した。タンタル、ニオブ、ランタン、ビスマス、カルシウム、クロム、マンガン、亜鉛を添加した場合には１.０Ｍの水酸化ナトリウム水溶液に投入し、３.５時間後に濾過後の残存重量が５０％を超えた。比較例４〜６との比較から明らかなように、これらの元素を添加することによりアルカリ性条件下における酸化タングステンの環境耐性が向上している。<Improvement of environmental resistance under alkaline conditions by adding elements other than copper>
Examples 5 to 12 and Comparative Examples 4 to 6 Addition of elements other than copper to tungsten oxide powder samples To investigate the effect of addition of elements other than copper, tungsten oxide powder (Wako Pure Chemical Industries, Ltd.) was used in the same manner as in the case of copper addition. ) Were mixed with a metal coating solution of each additive element purchased from the High-Purity Chemical Laboratory to a molar ratio of 0.05 with respect to tungsten, and each sample was prepared by baking at 800 ° C. for 1 hour. . When tantalum, niobium, lanthanum, bismuth, calcium, chromium, manganese, and zinc were added, they were put into a 1.0 M aqueous sodium hydroxide solution, and the remaining weight after filtration exceeded 50% after 3.5 hours. As is clear from comparison with Comparative Examples 4 to 6, the environmental resistance of tungsten oxide under alkaline conditions is improved by adding these elements.
〈銅以外の元素の添加の場合の光触媒活性について〉
（１）タンタルまたはニオブを添加した場合の光触媒活性
光触媒活性を調べるため、実施例５および６において調製したタンタルまたはニオブをタングステンに対してモル比で０.０５添加した酸化タングステンに助触媒として白金を０.１重量％添加し、それらを４.７ｍｌのバイアルびんにおよそ１５０ｍｇ入れ、これにアセトアルデヒドの気体を約７５００ｐｐｍ分加えて３００ＷのＸｅランプで光照射し、ガスクロマトグラフィーにより光分解で生じる二酸化炭素の量の時間変化をモニターした。図４および図５に結果を示す。なお、本例では、存在するアセトアルデヒドが完全に二酸化炭素にまで分解すると、およそ１５０００ｐｐｍの二酸化炭素が理論的に発生する。
図４および図５から分かるように、本発明のタンタルおよびニオブを添加した酸化タングステンは、アセトアルデヒドを分解することができ、光触媒活性を十分に保持していることが示された。
またタンタルおよびニオブを添加した酸化タングステンの実施例５および実施例６を１.０Ｍ水酸化ナトリウム水溶液で４時間処理したものについて、同様の試験を行い、アセトアルデヒトの光分解活性を調べた。その結果を、図４および図５に、水酸化ナトリウム水溶液で処理しない場合の結果と対比して示す。矢印で示したようにアルカリ性環境下における環境耐性を向上させるため、これらの元素を添加した酸化タングステンは、アルカリ処理することにより光触媒活性が著しく向上することが分かる。<Photocatalytic activity when elements other than copper are added>
(1) Photocatalytic activity when tantalum or niobium is added In order to investigate the photocatalytic activity, platinum as a cocatalyst is added to tungsten oxide in which tantalum or niobium prepared in Examples 5 and 6 is added at a molar ratio of 0.05 to tungsten. 0.1 wt%, and put about 150 mg of them into a 4.7 ml vial, add about 7500 ppm of acetaldehyde gas, and irradiate with a 300 W Xe lamp, and photolysis occurs by gas chromatography. The change over time in the amount of carbon dioxide was monitored. The results are shown in FIGS. In this example, when the existing acetaldehyde completely decomposes into carbon dioxide, approximately 15000 ppm of carbon dioxide is theoretically generated.
As can be seen from FIGS. 4 and 5, the tungsten oxide to which tantalum and niobium of the present invention were added was able to decompose acetaldehyde, and it was shown that the photocatalytic activity was sufficiently retained.
Further, the same test was conducted on the tungsten oxide examples 5 and 6 to which tantalum and niobium were added and treated with a 1.0 M aqueous sodium hydroxide solution for 4 hours, and the photolytic activity of acetaldehyde was investigated. The results are shown in FIG. 4 and FIG. 5 in comparison with the results when not treated with an aqueous sodium hydroxide solution. As indicated by the arrows, it can be seen that tungsten oxide to which these elements are added has a significantly improved photocatalytic activity when treated with an alkali in order to improve environmental resistance in an alkaline environment.
（２）ランタン、ビスマス、カルシウム、クロム、マンガンまたは亜鉛を添加した場合の光触媒活性
光触媒活性を調べるため、実施例７〜１２において調製したランタン、ビスマス、カルシウム、クロム、マンガンまたは亜鉛をタングステンに対してモル比で０.０５添加した酸化タングステンに助触媒として白金を０.１重量％添加し、それらを４.７ｍｌのバイアルびんにおよそ１５０ｍｇ入れ、これにアセトアルデヒドの気体を約８０００ｐｐｍ分加えて３００ＷのＸｅランプで光照射し、ガスクロマトグラフィーにより光分解で生じる二酸化炭素の量の時間変化をモニターした。図６に結果を示す。なお、本例では、存在するアセトアルデヒドが完全に二酸化炭素にまで分解すると、およそ１６０００ｐｐｍの二酸化炭素が理論的に発生する。
図６から分かるように、ビスマスをのぞき本発明のこれらの元素を添加した酸化タングステンは、アセトアルデヒドを分解することができ、光触媒活性を十分に保持していることが示された。また、ビスマスについては、後で示すようにランタンやタンタルなどと組み合わせて添加することにより光触媒活性を保持することができる。(2) Photocatalytic activity when lanthanum, bismuth, calcium, chromium, manganese, or zinc is added In order to investigate the photocatalytic activity, lanthanum, bismuth, calcium, chromium, manganese, or zinc prepared in Examples 7 to 12 was added to tungsten. As a cocatalyst, 0.1% by weight of platinum was added to tungsten oxide added at a molar ratio of 0.05, and approximately 150 mg of them was put into a 4.7 ml vial, to which about 8000 ppm of acetaldehyde gas was added to give 300 W. The Xe lamp was irradiated with light, and the time change of the amount of carbon dioxide generated by photolysis was monitored by gas chromatography. The results are shown in FIG. In this example, when the existing acetaldehyde completely decomposes into carbon dioxide, approximately 16000 ppm of carbon dioxide is theoretically generated.
As can be seen from FIG. 6, it was shown that tungsten oxide to which these elements of the present invention were added except bismuth can decompose acetaldehyde and sufficiently retain photocatalytic activity. Bismuth can retain photocatalytic activity by adding it in combination with lanthanum or tantalum, as will be described later.
また、上記の条件で光触媒活性が低かったビスマス添加の実施例８については、金属塗布液混合後の焼成温度を５００℃とすると光触媒活性の著しい向上が見られた。また、焼成温度を５００℃としても、得られたビスマス添加酸化タングステンはアルカリ性条件下において十分な環境耐性を有していた。
実施例８で焼成温度を５００℃とし、ビスマス添加量をタングステンに対するモル比でそれぞれ０.０１、０.０５、０.１０、０.１２、０.１５とした場合の、各ビスマス添加酸化タングステンのアルカリ性条件下における環境耐性を表３に示す。表３に示されるように、当該各ビスマス添加酸化タングステンについて、アルカリ性条件下で良好な環境耐性が得られている。なお、表３中の比較例５は、市販の酸化タングステン粉末に５００℃での焼成のみを行ったものである。Further, in Example 8 in which bismuth was added, which had low photocatalytic activity under the above conditions, a significant improvement in photocatalytic activity was observed when the firing temperature after mixing the metal coating solution was 500 ° C. Further, even when the firing temperature was 500 ° C., the obtained bismuth-added tungsten oxide had sufficient environmental resistance under alkaline conditions.
In Example 8, each bismuth-added tungsten oxide when the firing temperature is 500 ° C. and the bismuth addition amount is 0.01, 0.05, 0.10, 0.12, and 0.15 in terms of molar ratio to tungsten, respectively. Table 3 shows the environmental resistance under alkaline conditions. As shown in Table 3, each bismuth-added tungsten oxide has good environmental resistance under alkaline conditions. In addition, the comparative example 5 in Table 3 performed only baking at 500 degreeC to the commercially available tungsten oxide powder.
上述のとおり実施例８で焼成温度を５００℃とすることにより得られたビスマス添加酸化タングステンの光触媒活性を調べるため、ビスマスの添加量をタングステンに対してモル比で０.１０としたものについて、助触媒として白金を０.１重量％添加し、これにアセトアルデヒドの気体を約２０００ｐｐｍ分加えて３００ＷのＸｅランプからＬ42フィルターを通して可視光を照射し、ガスクロマトグラフィーにより光分解で生じる二酸化炭素の量の時間変化をモニターした。当該ビスマス添加タングステンを１.０Ｍ水酸化ナトリウム水溶液中に２４時間浸漬処理したものについても、同様に光触媒活性を調べた。また、上述の焼成温度を５００℃とした比較例５についても比較のため同様に光触媒活性を調べた。図７に結果を示す。なお、本例では、存在するアセトアルデヒドが完全に二酸化炭素にまで分解すると、およそ４０００ｐｐｍの二酸化炭素が理論的に発生する。図７から分かるように、この条件でビスマスを添加した酸化タングステンおよびこれをアルカリ処理した酸化タングステン（実施例８）は、１５０分程度の可視光照射によってアセトアルデヒドをほぼ完全に分解し、またその分解速度も５００℃で焼成しただけの何も添加していない酸化タングステン（比較例５）とほぼ同じであり、光触媒活性を十分に保持していることが示された。
このように、酸化タングステン粉末に金属塗布液などを含浸して焼成することによりビスマスを添加する場合は、焼成温度は好ましくは４００〜７００℃、より好ましくは４５０〜５５０℃であり、前記した、同様の方法で銅を添加する場合の好ましい焼成温度とは異なっており、このことは最適な焼成温度が添加する元素の種類に依存することを示している。As described above, in order to examine the photocatalytic activity of the bismuth-added tungsten oxide obtained by setting the firing temperature in Example 8 to 500 ° C., the addition amount of bismuth was set to 0.10 in molar ratio to tungsten. The amount of carbon dioxide generated by photolysis by gas chromatography after adding 0.1% by weight of platinum as a co-catalyst, adding about 2000 ppm of acetaldehyde gas, irradiating visible light through a L42 filter from a 300 W Xe lamp. The time change of was monitored. The photocatalytic activity of the bismuth-added tungsten immersed in a 1.0 M aqueous sodium hydroxide solution for 24 hours was similarly examined. In addition, the photocatalytic activity was similarly examined for Comparative Example 5 in which the above-described calcination temperature was 500 ° C. for comparison. The results are shown in FIG. In this example, when the existing acetaldehyde completely decomposes into carbon dioxide, approximately 4000 ppm of carbon dioxide is theoretically generated. As can be seen from FIG. 7, tungsten oxide to which bismuth was added under this condition and tungsten oxide obtained by alkali treatment (Example 8) decomposed acetaldehyde almost completely by visible light irradiation for about 150 minutes, and the decomposition thereof. The rate was almost the same as that of tungsten oxide (Comparative Example 5) that was baked at 500 ° C. and nothing was added, and it was shown that the photocatalytic activity was sufficiently maintained.
Thus, when adding bismuth by impregnating a tungsten oxide powder with a metal coating solution and firing, the firing temperature is preferably 400 to 700 ° C., more preferably 450 to 550 ° C., This is different from the preferred firing temperature when copper is added in a similar manner, indicating that the optimum firing temperature depends on the type of element added.
さらに実施例８で焼成温度を５００℃、ビスマスの添加量をタングステンに対してモル比で０.０１〜０.１２としたものについて、助触媒として白金を０．１重量％添加し、これにアセトアルデヒドの気体を約２０００ｐｐｍ分加えて３００ＷのＸｅランプからＬ42フィルターを通して可視光を照射し、２０分後における二酸化炭素の生成量を調べた。比較のため比較例５で焼成温度を５００℃としたものについても同様に二酸化炭素の生成量を調べた。図８に結果を示す。ビスマスの添加によりアセトアルデヒドの分解により生成する二酸化炭素の量は無添加の比較例５の場合より増加しており、ビスマスの添加により酸化タングステンの光触媒活性が向上していることが分かる。比較的にビスマスの添加量が少ない領域において、無添加の場合に対する光触媒活性の向上が見られた。この場合のビスマスの添加量は、タングステンに対するモル比で、好ましくは０.００５〜０.１５、より好ましくは０.０１〜０.１２であった。表３から分かるように、光触媒活性の向上が見られるような比較的にビスマスの添加量が少ない場合でも、無添加の場合と比較するとアルカリ性条件下における環境耐性は向上する。 Further, in Example 8 where the calcination temperature was 500 ° C. and the addition amount of bismuth was 0.01 to 0.12 in terms of molar ratio to tungsten, 0.1% by weight of platinum was added as a co-catalyst. About 2000 ppm of acetaldehyde gas was added and irradiated with visible light from a 300 W Xe lamp through an L42 filter, and the amount of carbon dioxide produced after 20 minutes was examined. For comparison, the amount of carbon dioxide produced in Comparative Example 5 with a firing temperature of 500 ° C. was also examined. The results are shown in FIG. The amount of carbon dioxide produced by the decomposition of acetaldehyde by the addition of bismuth is increased compared to the case of Comparative Example 5 without addition, and it can be seen that the photocatalytic activity of tungsten oxide is improved by the addition of bismuth. In the region where the amount of bismuth added was relatively small, the photocatalytic activity was improved compared to the case where no bismuth was added. In this case, the amount of bismuth added was preferably 0.005 to 0.15, more preferably 0.01 to 0.12, in terms of a molar ratio to tungsten. As can be seen from Table 3, even when the amount of bismuth added is relatively small so that the photocatalytic activity is improved, the environmental resistance under alkaline conditions is improved as compared with the case of no addition.
〈薄膜形状の酸化タングステンに銅以外の元素を添加した場合のアルカリ性条件下における環境耐性の向上について（元素の単独および複合添加）〉
ランタンまたはビスマスを単独で、および、それらを複合して添加した場合
実施例１の場合に用いたＰＡ法の過酸化ポリタングステンを導電性ガラス上にスピンコートにより製膜して５００℃で焼成することで酸化タングステン薄膜を作製した。この薄膜にランタンまたはビスマスの金属塗布液をスピンコートし、５００℃で焼成してそれぞれ実施例１３および実施例１４とした。また酸化タングステン薄膜に最初にランタンの金属塗布液をスピンコートして５００℃で焼成してから希釈したビスマスの金属塗布液をスピンコートしてさらに５００℃で焼成することによってランタンとビスマスを複合添加した酸化タングステン薄膜を作製した。ビスマスの金属塗布液（原液のビスマス濃度０.５Ｍ）を酢酸ブチルで希釈し、スピンコートする塗布液の濃度が０.２Ｍのものを実施例１５、０.１Ｍのものを実施例１６、０.０４Ｍのものを実施例１７、０.０２Ｍのものを実施例１８とした。実施例１６〜１８はさらに塩化白金酸を塗布して３００℃で焼成し、白金を助触媒として担持させた。同様の方法で作製した何も添加しない酸化タングステン薄膜を比較例７とした。
アルカリ性条件下における環境耐性の向上を調べるため１.０Ｍの水酸化ナトリウム水溶液に投入し、３０分経過後の酸化タングステンの残存量を測定した。結果を表３に示す。ランタン添加の実施例１３ではおよそ９０％が残り、ビスマス添加の実施例１４ではおよそ８０％が残った。さらにランタンとビスマスを複合添加した実施例１５〜１８ではすべて９０％以上が残った。一方、何も添加しなかった比較例７では全く酸化タングステンは残っていない。このことから薄膜形状の酸化タングステンにおいても元素添加によりアルカリ性条件下における環境耐性が向上することが分かる。また複数の元素を複合して添加することによってもアルカリ性条件下における環境耐性が向上することも分かった。<Improvement of environmental resistance under alkaline conditions when elements other than copper are added to thin-film tungsten oxide (elemental and composite additions)>
When lanthanum or bismuth is added singly or in combination thereof PA polytungsten peroxide of the PA method used in Example 1 is formed on a conductive glass by spin coating and baked at 500 ° C. Thus, a tungsten oxide thin film was produced. This thin film was spin-coated with a lanthanum or bismuth metal coating solution and baked at 500 ° C. to obtain Examples 13 and 14, respectively. The tungsten oxide thin film is first spin-coated with a lanthanum metal coating solution and baked at 500 ° C., and then diluted with a diluted bismuth metal coating solution and further baked at 500 ° C. to add lanthanum and bismuth. A tungsten oxide thin film was prepared. A metal coating solution of bismuth (diluted bismuth concentration of 0.5M) is diluted with butyl acetate, and the spin coating solution concentration is 0.2M in Example 15, 0.1M solution in Example 16, 0. The .04M sample was designated as Example 17, and the 0.02M sample was designated as Example 18. In Examples 16 to 18, chloroplatinic acid was further applied and baked at 300 ° C., and platinum was supported as a promoter. A tungsten oxide thin film prepared by the same method without any addition was designated as Comparative Example 7.
In order to investigate the improvement of environmental resistance under alkaline conditions, the solution was added to a 1.0 M sodium hydroxide aqueous solution, and the remaining amount of tungsten oxide after 30 minutes was measured. The results are shown in Table 3. Approximately 13% remained in Example 13 with lanthanum, and approximately 80% remained in Example 14 with bismuth addition. Furthermore, in Examples 15 to 18 in which lanthanum and bismuth were added in combination, 90% or more remained. On the other hand, no tungsten oxide remains in Comparative Example 7 in which nothing was added. From this, it can be seen that even in the case of thin-film tungsten oxide, environmental resistance under alkaline conditions is improved by addition of elements. It was also found that the environmental resistance under alkaline conditions is improved by adding a plurality of elements in combination.
〈薄膜形状の酸化タングステンに銅以外の元素を添加した場合の光触媒活性について〉
光触媒活性を調べるため、先に助触媒として白金を製膜した導電性ガラスに酸化タングステン、ランタン、ビスマス（０.１Ｍに希釈）を上記の方法により順に製膜したものを実施例１９、またランタンの代わりにタンタルを用いたものを実施例２０として、それらを市販のアルカリ性カビ除去剤（ジョンソン株式会社 カビキラー：水酸化ナトリウム濃度０.１２５Ｍ）で６時間処理したものおよび処理しないものを用いてアセトアルデヒトの光分解を行った。アセトアルデヒドの気体を約５００ｐｐｍ分加えて３００ＷのＸｅランプＬ42フィルターを通して光照射し、ガスクロマトグラフィーにより光分解で生じる二酸化炭素の量の時間変化をモニターした。また比較のため先に助触媒として白金を製膜した導電性ガラスに酸化タングステンのみを製膜したものを比較例８としての同様の光分解を行った。図９および図１０に結果を示す。なお、本例では、存在するアセトアルデヒドが完全に二酸化炭素にまで分解すると、およそ１０００ｐｐｍの二酸化炭素が理論的に発生する。
ランタンとビスマスを複合的に添加した実施例１９、タンタルとビスマスを複合的に添加した実施例２０においても比較例８と比較してアルカリ暴露後も含めて光触媒活性が失われていないこと、またアルカリ処理により光触媒活性が向上することが確かめられた。本実施例では、粉末形状の場合と同じく、気相中のアセトアルデヒトの分解除去について示したが、本発明の酸化タングステン光触媒薄膜を用いて、光触媒作用によって表面に付着した有機物を分解除去するセルフクリーニング機能を発現させることも可能である。<Photocatalytic activity when elements other than copper are added to thin-film tungsten oxide>
In order to investigate the photocatalytic activity, tungsten oxide, lanthanum, and bismuth (diluted to 0.1M) were sequentially formed on the conductive glass previously formed with platinum as a cocatalyst by the above method in Example 19, and lanthanum. Example 20 was obtained by using tantalum instead of acetoside, and those treated with a commercially available alkaline mold remover (Johnson Co., Ltd., mold killer: sodium hydroxide concentration of 0.125 M) for 6 hours and those not treated with aceto Aldecht was photodegraded. About 500 ppm of acetaldehyde gas was added and irradiated with light through a 300 W Xe lamp L42 filter, and the change over time in the amount of carbon dioxide produced by photolysis was monitored by gas chromatography. For comparison, the same photodecomposition as Comparative Example 8 was performed on a conductive glass in which only tungsten oxide was formed on a conductive glass previously formed with platinum as a promoter. The results are shown in FIG. 9 and FIG. In this example, when the existing acetaldehyde completely decomposes into carbon dioxide, approximately 1000 ppm of carbon dioxide is theoretically generated.
In Example 19 in which lanthanum and bismuth were added in a composite manner, and in Example 20 in which tantalum and bismuth were added in a composite manner, the photocatalytic activity was not lost even after exposure to alkali as compared with Comparative Example 8. It was confirmed that the photocatalytic activity was improved by the alkali treatment. In this example, as in the case of powder form, the decomposition and removal of acetaldehyde in the gas phase was shown, but the self-catalyst that decomposes and removes organic substances adhering to the surface by photocatalysis using the tungsten oxide photocatalytic thin film of the present invention. It is also possible to develop a cleaning function.
本発明のアルカリ性条件下における可視光応答性光触媒の環境耐性を向上させる方法を用いることにより、これまで洗剤などに暴露されてアルカリ性や酸性となるために、環境耐性が低い可視光応答性光触媒を使用できなかった流し台、浴室、トイレなどの壁面やそれらの場所で使用するその他の製品表面に、可視光応答性光触媒として銅添加酸化タングステンを使用することができるようになる。これらにおいてセルフクリーニング材料としてこの可視光応答性光触媒を用いることで、その表面を清浄に保つことが可能になる。 By using the method for improving the environmental resistance of a visible light responsive photocatalyst under alkaline conditions of the present invention, a visible light responsive photocatalyst with low environmental resistance is obtained because it has been exposed to a detergent or the like to become alkaline or acidic. Copper-doped tungsten oxide can be used as a visible light responsive photocatalyst on walls such as sinks, bathrooms, and toilets that could not be used, and other product surfaces used in those places. In these, by using the visible light responsive photocatalyst as a self-cleaning material, the surface can be kept clean.
Claims (6)
前記酸化タングステンの前駆体に前記元素の少なくともいずれかを加えて混合して焼成する工程、前記酸化タングステンの粉末に前記元素の少なくともいずれかを含む溶液を含浸して焼成する工程、及び前記酸化タングステンの膜に前記溶液を塗布して焼成する工程のいずれかの焼成工程を含むことを特徴とする方法。 Tantalum tungsten oxide, La lanthanum, bismuth, by adding alone or in combination with elements of calcium, there a way of improving the environmental resistance in alkaline conditions without losing the photocatalytic function by visible light of the tungsten oxide And
Adding at least one of the above elements to the tungsten oxide precursor and mixing and firing; step of impregnating the tungsten oxide powder with a solution containing at least one of the elements; and firing the powder; and tungsten oxide A method comprising a baking step of any of the steps of applying the solution to the film and baking.
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| US20130324393A1 (en) | 2013-12-05 |
| EP2676729B1 (en) | 2019-04-10 |
| JPWO2012111709A1 (en) | 2014-07-07 |
| KR20130123442A (en) | 2013-11-12 |
| WO2012111709A1 (en) | 2012-08-23 |
| EP2676729A4 (en) | 2014-12-24 |
| US9533284B2 (en) | 2017-01-03 |
| KR101554236B1 (en) | 2015-09-18 |
| CN103370132B (en) | 2016-05-18 |
| EP2676729A1 (en) | 2013-12-25 |
| CN103370132A (en) | 2013-10-23 |
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